Italy

This paper assesses the optimal design criteria of a flexible power and biomass to methanol (PBtM) plant conceived to operate both without green hydrogen addition (baseline mode) and with hydrogen addition (enhanced mode) following an intermittent use of the electrolysis system which is turned on when the electricity price allows an economically viable hydrogen production. The assessed plant includes a gasification section syngas cleaning and compression methanol synthesis and purification and heat recovery steam cycle to be flexibly operated. A sorption-enhanced gasification technology allows to produce a tailored syngas for the downstream synthesis in both the baseline and enhanced operating conditions by controlling the in-situ CO2 separation rate. Two designs are assessed for the methanol synthesis unit with two different reactor sizes: (i) a larger reactor designed on the enhanced operation mode (enhanced reactor design – ERD) and (ii) a smaller reactor designed on the baseline operation mode (baseline reactor design – BRD). The ERD design resulted to be preferable from the techno economic perspectives resulting in 20% lower cost of the e-MeOH (30.80 vs. 37.76 €/ GJLHV) with the baseline assumptions (i.e. 80% of electrolyzer capacity factor and 2019 Denmark day-ahead market electricity price). Other important outcomes are: (i) high electrolysis capacity factor is needed to obtain competitive cost of e-MeOH and (ii) advantages of flexibly operated PBtM plants with respect to inflexible PBtM plants are significant in scenarios with high penetration of intermittent renewables leading to low average prices of electricity but also longer periods of high peak prices.

Hydrogen is one of the most suitable candidates in replacing fossil fuels. However storage issues due to its very low density under ambient conditions are encountered in many applications. The liquefaction process can overcome such issues by increasing hydrogen’s density and thus enhancing its storage capacity. A boiling liquid expanding vapour explosion (BLEVE) is a phenomenon in liquefied gas storage systems. It is a physical explosion that might occur after the catastrophic rupture of a vessel containing a liquid with a temperature above its boiling point at atmospheric pressure. Even though it is an atypical accident scenario (low probability) it should be always considered due to its high yield consequences. For all the above-mentioned reasons the BLEVE phenomenon for liquid hydrogen (LH2) vessels was studied using the CFD methodology. Firstly the CFD model was validated against a well-documented CO2 BLEVE experiment. Secondly hydrogen BLEVE cases were simulated based on tests that were conducted in the 1990s on LH2 tanks designed for automotive purposes. The parametric CFD analysis examined different filling degrees initial pressures and temperatures of the tank content with the aim of comprehending to what extent the initial conditions influence the blast wave. Good agreement was shown between the simulation outcomes and the LH2 bursting scenario tests results.

Hydrogen Embrittlement (HE) is a topical issue for pipelines transporting sour products. Engineers need a simple and effective approach in materials selection at design stage. In other words they must know if a material is susceptible to cracking to be able of:

• selecting the right material 
• and apply correct operational measures during the service life.

Following ASTM F2078 HE is “a permanent loss of ductility in a metal or alloy caused by hydrogen in combination with stress either externally applied or internal residual stress”. In many cases hydrogen can play a role in crack propagation as for instance in Stress Corrosion Cracking (SCC) and Corrosion Fatigue (CF). Three parameters are required to cause failure: presence of hydrogen tensile stress and material susceptibility. The two previous ones are triggering the failure while the root cause is usually material susceptibility. This is why material selection is the important step to safely manage engineering structural materials.

As an example material selection for sour service pipeline is the object of well-known standards e.g. by Nace International and EFC: they pose some limits in the sour service of steels with reference to surface hardness. These standards have shown some weak points namely:

• In the definition of sour service;
• In defining the role of crack initiation and propagation considering that in Hydrogen embrittlement stress state and stress variations are very important.

As for the second point in hydrogen generation anodic processes shall be taken into account too. For instance there is a relationship between corrosion resistance and crack susceptibility. In carbon and low alloy steels cracking will not normally occur when there is a significant corrosion rate. If a brittle layer (or a brittle spot) is present on the metal surface this one can initiate a crack.

In the pathway towards decarbonization hydrogen can provide valid support in different sectors such as transportation iron and steel industries and domestic heating concurrently reducing air pollution. Thanks to its versatility hydrogen can be produced in different ways among which steam reforming of natural gas is still the most commonly used method. Today less than 0.7% of global hydrogen production can be considered low-carbon-emission. Among the various solutions under investigation for low-carbon hydrogen production membrane reactor technology has the potential especially at a small scale to efficiently convert biogas into green hydrogen leading to a substantial process intensification. Fluidized bed membrane reactors for autothermal reforming of biogas have reached industrial maturity. Reliable modelling support is thus necessary to develop their full potential. In this work a mathematical model of the reactor is used to provide guidelines for their design and operations in off-design conditions. The analysis shows the influence of temperature pressures catalyst and steam amounts and inlet temperature. Moreover the influence of different membrane lengths numbers and pitches is investigated. From the results guidelines are provided to properly design the geometry to obtain a set recovery factor value and hydrogen production. For a given reactor geometry and fluidization velocity operating the reactor at 12 bar and the permeate-side pressure of 0.1 bar while increasing reactor temperature from 450 to 500 °C leads to an increase of 33% in hydrogen production and about 40% in HRF. At a reactor temperature of 500 °C going from 8 to 20 bar inside the reactor doubled hydrogen production with a loss in recovery factor of about 16%. With the reactor at 12 bar a vacuum pressure of 0.5 bar reduces hydrogen production by 43% and HRF by 45%. With the given catalyst it is sufficient to have only 20% of solids filled into the reactor being catalytic particles. With the fixed operating conditions it is worth mentioning that by adding membranes and maintaining the same spacing it is possible to increase hydrogen production proportionally to the membrane area maintaining the same HRF.

A numerical study of the energy conversion process occurring in a lean-charge cogenerative engine designed to be powered by natural gas is here conducted to analyze its performances when fueled with mixtures of natural gas and several percentages of hydrogen. The suitability of these blends to ensure engine operations is proven through a zero–one-dimensional engine schematization where an original combustion model is employed to account for the different laminar propagation speeds deriving from the hydrogen addition. Guidelines for engine recalibration are traced thanks to the achieved numerical results. Increasing hydrogen fractions in the blend speeds up the combustion propagation achieving the highest brake power when a 20% of hydrogen fraction is considered. Further increase of this last would reduce the volumetric efficiency by virtue of the lower mixture density. The formation of the NOx pollutants also grows exponentially with the hydrogen fraction. Oppositely the efficiency related to the exploitation of the exhaust gases’ enthalpy reduces with the hydrogen fraction as shorter combustion durations lead to lower temperatures at the exhaust. If the operative conditions are shifted towards leaner air-to-fuel ratios the in-cylinder flame propagation speed decreases because of the lower amount of fuel trapped in the mixture reducing the conversion efficiencies and the emitted nitrogen oxides at the exhaust. The link between brake power and spark timing is also highlighted: a maximum is reached at an ignition timing of 21° before top dead center for hydrogen fractions between 10 and 20%. However the exhaust gases’ temperature also diminishes for retarded spark timings. Lastly an optimization algorithm is implemented to individuate the optimal condition in which the engine is characterized by the highest power production with the minimum fuel consumption and related environmental impact. As a main result hydrogen addition up to 15% in volume to natural gas in real cogeneration systems is proven as a viable route only if engine operations are shifted towards leaner air-to-fuel ratios to avoid rapid pressure rise and excessive production of pollutant emissions.

Supporting policies to achieve a green revolution and ecological transition is a global trend. Although the maritime transport of goods and people can rightly be counted among the least polluting sectors much can be done to further reduce its environmental footprint. Moreover to boost the ecological transition of vessels a whole series of international regulations and national laws have been promulgated. Among these the most impactful on both design and operational management of ships concern the containment of air-polluting emissions in terms of GHG NOx SOx and PM. To address this challenge it might seem that many technologies already successfully used in other transport sectors could be applied. However the peculiar characteristics of ships make this statement not entirely true. In fact technological solutions recently adopted for example in the automotive sector must deal with the large size of vessels and the consequent large amount of energy necessary for their operation. In this paper with reference to the case study of a medium/large-sized passenger cruise ship the use of different fuels (LNG ammonia hydrogen) and technologies (internal combustion engines fuel cells) for propulsion and energy generation on board will be compared. By imposing the design constraint of not modifying the payload and the speed of the ship the criticalities linked to the use of one fuel rather than another will be highlighted. The current limits of application of some fuels will be made evident with reference to the state of maturity of the relevant technologies. Furthermore the operational consequences in terms of autonomy reduction will be presented. The obtained results underline the necessity for shipowners and shipbuilders to reflect on the compromises required by the challenges of the ecological transition which will force them to choose between reducing payload or reducing performance.

Hybrid electric vehicles are currently one of the most effective ways to increase the efficiency and reduce the pollutant emissions of internal combustion engines. Green hydrogen produced with renewable energies is an excellent alternative to fossil fuels in order to drastically reduce engine pollutant emissions. In this work the author proposes the implementation of a hydrogen-fueled engine in a hybrid vehicle; the investigated hybrid powertrain is the power-split type in which the engine two electric motor/generators and the drive shaft are coupled together by a planetary gear set; this arrangement allows the engine to operate independently from the wheels and thus to exploit the best efficiency operating points. A set of numeric simulations were performed in order to compare the gasoline-fueled engine with the hydrogen-fueled one in terms of the thermal efficiency and total energy consumed during a driving cycle. The simulation results show a mean engine efficiency increase of around 17% when fueled with hydrogen with respect to gasoline and an energy consumption reduction of around 15% in a driving cycle.

The development of more sustainable and zero-emissions collective transport solutions could play a very important measure in the near future within smart city policies. This paper tries to give a contribution to this aim proposing a novel approach to fuel cell vehicle design and operation. Traditional difficulties experienced in fuel cell transient operation are in fact normally solved in conventional vehicle prototypes through the hybridization of the propulsion system and with the complete fulfillment of transients in road energy demand through a high-capacity onboard energy storage device. This makes it normally necessary to use Li-ion battery solutions accepting their restrictions in terms of weight costs energy losses limited lifetime and environmental constraints. The proposed solution instead introduces a partitioning of the hydrogen fuel cell (FC) and novel optimal power control strategy with the aim of limiting the capacity of the energy storage still avoiding FC transient operation. The limited capacity of the resulting energy storage systems which instead has to answer higher power requests makes it possible to consider the utilization of a high-speed flywheel energy storage system (FESS) in place of high energy density Li-ion batteries. The proposed control strategy was validated by vehicle simulations based on a modular and parametric model; input data were acquired experimentally on an operating electric bus in real traffic conditions over an urban bus line. Simulation results highlight that the proposed control strategy makes it possible to obtain an overall power output for the FC stacks which better follows road power demands and a relevant downsizing of the FESS device.

This paper contributes to the climate policy discussion by focusing on the challenges and opportunities of reaching net zero emissions by 2050 in Italy. To support Italian energy planning we developed energy roadmaps towards national climate neutrality consistent with the Paris Agreement objectives and the IPCC goal of limiting the increase in global surface temperature to 1.5 ◦C. Starting from the Italian framework these scenarios identify the correlations among the main pillars for the change of the energy paradigm towards net emissions by 2050. The energy scenarios were developed using TIMES-RSE a partial equilibrium and technology-rich optimization model of the entire Italian energy system. Subsequently an in-depth analysis was developed with the sMTISIM a long-term simulator of power system and electricity markets. The results show that to achieve climate neutrality by 2050 the Italian energy system will have to experience profound transformations on multiple and strongly related dimensions. A predominantly renewable-based energy mix (at least 80–90% by 2050) is essential to decarbonize most of the final energy consumption. However the strong increase of non-programmable renewable sources requires particular attention to new flexibility resources needed for the power system such as Power-to-X. The green fuels produced from renewables via Power-to-X will be a vital energy source for those sectors where electrification faces technical and economic barriers. The paper’s findings also confirm that the European “energy efficiency first” principle represents the very first step on the road to climate neutrality.

The competitiveness of biofuels may be increased by integrating biomass gasification plants with electrolysis units which generate hydrogen to be combined with carbon-rich syngas. This option allows increasing the yield of the final product by retaining a higher amount of biogenic carbon and improving the resilience of the energy sector by favoring electric grid services and sector coupling. This article illustrates a techno-economic comparative analysis of three flexible power and biomass to methanol plants based on different gasification technologies: direct gasification indirect gasification and sorptionenhanced gasification. The design and operational criteria of each plant are conceived to operate both without green hydrogen addition (baseline mode) and with hydrogen addition (enhanced mode) following an intermittent use of the electrolysis system which is turned on when the electricity price allows an economically viable hydrogen production. The methanol production plants include a gasification section syngas cleaning conditioning and compression section methanol synthesis and purification and heat recovery steam cycle to be flexibly operated. Due to the high oxygen demand in the gasifier the direct gasification-based plant obtains a great advantage to be operated between a minimum load to satisfy the oxygen demand at high electricity prices and a maximum load to maximize methanol production at low electricity prices. This allows avoiding large oxygen storages with significant benefits for Capex and safety issues. The analysis reports specific fixed-capital investments between 1823 and 2048 €/kW of methanol output in the enhanced operation and LCOFs between 29.7 and 31.7 €/GJLHV. Economic advantages may be derived from a decrease in the electrolysis capital investment especially for the direct gasification-based plants which employ the greatest sized electrolyzer. Methanol breakeven selling prices range between 545 and 582 €/t with the 2019 reference Denmark electricity price curve and between 484 and 535 €/t with an assumed modified electricity price curve of a future energy mix with increased penetration of intermittent renewables.